MR thermometry based on magnetic nanoparticle Para-Phase

This study reports a magnetic resonance (MR) thermometer based on the paramagnetic phase (Para-Phase) of magnetic nanoparticles (MNPs). The magnetocaloric effect of MNPs can be characterized by magnetic susceptibility and further mapped into the MRI echo signal phase. The effects of particle size, concentration, MRI field strength, and Echo Time (TE) on Para-Phase were analyzed. The results indicate that lower field excitation, smaller particle size, and higher concentration MNPs exhibit higher temperature sensitivity in the Para-Phase. Temperature experiments under different magnetic fields were designed. The temperature measurement accuracy of 3T-MRI is better than 0.1K within the physiological temperature range. Although 0.5T-MRI theoretically has higher sensitivity, its temperature measurement effect is not good because the image signal-to-noise ratio (SNR) and system field drift far worse than 3T. But it is also sufficient to achieve a temperature measurement uncertainty of 0.2K.